Valency

The valency (or valence) of an atom determines the number of bonds that it can form with other atoms. For example, a valency of 1 indicates that an atom can only form a bond with one other atom; a valency of 3 that it can form bonds with three other atoms, etc. We say that an atom is monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent etc.

The noble gases (helium, neon, argon, krypton, xenon, radon),have a valency of 0 and therefore only occur naturally in the monatomic form.